I was putting up some wall decorations earlier today and was painstakingly realigning everything until it looked level to my eyes. It might be just a hair off, but if I don’t correct it, I’ll see the misalignment almost instantly and get bothered for the rest of time until I fix it. Has anyone investigated, or is there literature on the minimum perceptible angle from level to the naked eye?
I think it depends on 1) the person and 2) the context and 3) the desired precision. I would use an actual level to test against my intuition before I’d have confidence in it.